Rubber additives

ABSTRACT

Aliphatic alcohols, esters of such alcohols and aliphatic dicarboxylic acids, mixtures of such alcohols and esters and mixtures of such alcohols and esters with aliphatic carboxylic acids are used as additives in the vulcanization of rubbers.

This is a continuation of application Ser. No. 496,611 filed Aug. 12, 1974 now abandoned.

FIELD OF THE INVENTION

Stearic acid and other aliphatic long-chain monocarboxylic acids containing substantially 12 to 18 carbon atoms such as lauric acid, oleic acid and palmitic acid, etc. have been widely used as activators of the acceleration of the vulcanization of olefinic rubber. This invention relates to the vulcanization of such rubber with sulphur and an accelerator and an additive which may replace at least a part of the stearic or other such acid used in rubber mixes.

PRIOR ART

Although stearic acid is the principle vulcanization activator, other long chain monocarboxylic acids including oleic acid and lauric acid, and mixtures of acids from cottonseed, linseed, cocoanut, soybean, treated tallow and fishoils, etc. have been marketed for use as activators.

SUMMARY OF THE INVENTION

According to this invention, at least a part of the stearic or other long-chain monocarboxylic acid used as an activator in the vulcanization of olefinic rubbers is replaced by a substantial amount of (a) an aliphatic alcohol containing 12 to 28 carbon atoms; (b) an ester of such an alcohol and a carboxylic acid containing 4 to 22 or as many as 54 carbon atoms; (c) a mixture of a substantial amount of such an alcohol and a substantial amount of such a carboxylic acid; (d) a mixture of a substantial amount of such an ester with a substantial amount of such a carboxylic acid and (e) a mixture of a substantial amount of such an alcohol, a substantial amount of such a carboxylic acid and a substantial amount of such an ester. The compounds or mixtures are non-volatile at 150° to 200° F. or at whatever the temperature to which the rubber mix is heated.

As with stearic acid, the replacement additives bring about improved functioning of the sulfur, zinc oxide and other compounding ingredients in the rubber mix. The exact mechanism is not understood.

The term "olefinic rubber" is used herein to include natural rubber and the synthetic rubbers derived at least in part from a conjugated diene or other olefin.

The carboxylic acids may be used (1) to mix with, and/or to react with, the long-chain alcohols to form esters containing one to three or more carboxylic acid groups, and (2) to mix with such esters with or without such an alcohol, are aliphatic hydrocarbon (either branched or straight chain, saturated or unsaturated, cyclic or acylic) or aromatic in character, and may contain aromatic or aliphatic hydrocarbon residues. They must contain at least four carbon atoms including the carboxylic acid groups, and may contain as many as 22 carbon atoms. Examples of the carboxylic acids are given below:

    ______________________________________                                         Monocarboxylic                                                                              Dicarboxylic  Tricarboxylic                                       ______________________________________                                         Butyric      Succinic      Aconitic                                            Valeric      Glutaric      Citric                                              Hexanoic (caproic)                                                                          Adipic        Tricarballylic                                      Hepanoic     Pimelic       Trimer oleic acid                                   Octanoic (caprylic)                                                                         Suberic       Trimellitic                                         Pelargonic   Azelaic                                                           Capric       Sebacic                                                           Undeconoic   Dodecanedioic                                                     Lauric       Brassylic                                                         Myristic     Thapsic                                                           Palmitic     Phthalic                                                          Stearic      Isophthalic                                                       Behenic      Terephthalic                                                      Naphthenic   Maleic                                                                         21-Acid*                                                                       Dimer oleic                                                       ______________________________________                                          *21-Acid is the mixture of acid produced according to U.S. Pat. No.            3,753,968.                                                               

and dimers thereof and C-12 dibasic acids which result from the polymerization of unsaturated fatty acids and the like.

The long chain alcohols which may be used (1) alone or (2) in esterifying the acids or (3) in admixture such an acid and/or ester, are saturated or unsaturated, straight-chain or branched-chain aliphatics and include at least 12 carbon atoms, and may contain up to 28 or more carbon atoms. The shorter chain alcohols are too volatile and may emit disagreeable odors. These long chain alcohols include lauryl, alcohol, myristyl, stearyl, eicosyl, cetyl alcohol, behenyl alcohol, and also the odd-chain tridecyl, pentodecanyl, heptodecyl and monodecyl alcohols. The reference to the long-chain alcohols herein includes alcoholic bottoms such as, for example, those resulting from the oxo processes and processes in which alcohols are manufactured from alpha-olefins and from the hydrogenation of fats and oils. They include the branched chain and iso-alcohols, and may be secondary alcohols, but not tertiary alcohols, if used for esterification with a carboxylic such as just described.

By-product alcohols are included, such as Alfol® 20+ and Alfol® 22+ obtainable from Petrochemical Department of Continentoal Oil Co. and Epal® C-20+ alcohols from the Ethyl Corporation. Their homolog distribution, on 100% alcohol basis as determined by gas--liquid chromatography is, approximately:

    ______________________________________                                         Alcohol      Alfol 20+ Epal C-20+ Alfol 22+                                    ______________________________________                                         C.sub.18 and lower                                                                           2%       0-2         1%                                          C.sub.20     60        10-20       5                                           C.sub.22     20        10-15      60                                           C.sub.24     10         5-15      21                                           C.sub.26      5         8-12       9                                           C.sub.28 and higher                                                                          3        11-30       4                                                        100%      --         100%                                         Normal alcohols                                                                             71        33         60                                           Branched alcohols                                                                           18        34         10                                           Hydrocarbons  9        30         30                                           Esters        2         3          3                                           ______________________________________                                    

Typical properties are given as:

    ______________________________________                                                     Alfol 20+                                                                              Epal C-20+ Alfol 22+                                       ______________________________________                                         Alcohol content,                                                                             70        67         60                                          approximate                                                                    Hydroxyl number                                                                              123       100        90                                          Saponification number                                                                        3         1.6        6                                           Iodine number 12        9          13                                          Carboxy, % (As C=0)                                                                          0.2       .16        0.3                                         Water, %      0.05      --         0.03                                        Melting range, ° C.                                                                   45-57     45 (min)   45-65                                       Color, Gardner, Molten                                                                       12        4          18                                          ______________________________________                                    

Such materials classify as long-chain alcohols as herein contemplated. They include at least substantially 50% of alcohols which contain at least 12 carbon atoms.

Heavy oxo-ends are also included as alcohols herein. The properties and analysis of such heavy oxo-ends follow:

    ______________________________________                                         Boiling range at 20 mm. Hg. pressure                                                                  143°-316° C.                              Specific Gravity       0.840-0.880                                             GC analysis:                                                                   C.sub.11 alcohol       14.4%                                                   C.sub.13 alcohol        8.3%                                                   Longer chain alcohols, ethers, glycols                                                                76.3%                                                   Hydroxyl No.           226 ± 10                                             ______________________________________                                    

Only those oxo-ends which are substantially non-volatile at 200° F. are usable alone, and for admixture with the other additives referred to herein, the boiling range of the oxo-end should be such that the total additive is non-volatile at substantially 200° F.

The acid number of an acid and the saponification number of an ester, to which this invention relates, is at least 50.

The acid number or saponification number is defined as the number of milligrams of potassium hydroxide which will react with 1 gram of the substance. Acid value refers to free acidity of carboxylic groups, while saponification value refers to the carboxylic groups tied up as esters.

The results of the examples which follow show that the addition of acid may retard the rate of the cure of a rubber mix. The addition of alcohol may not retard the cure of a rubber mix. The addition of alcohol may not retard the cure as much as stearic acid; it improves the physical properties of the mix and/or vulcanizate. The addition of ester such as that to which the invention relates improves processing and absorption of pigment.

The additive is used in mixes of natural rubber and synthetic olefinic rubbers which contain sulfur and zinc oxide in substantially the proportion which is usual for stearic acid. Some stearic acid may be used in the rubber mix, and then less additive is required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rheograph comparing the composition of EXAMPLE VI having 2 parts ALFOL 20+ with the composition of EXAMPLE VI having 2 parts of stearic acid.

FIG. 2 is a rheograph comparing the composition of EXAMPLE VI having 6 parts ALFOL 20+ with the composition of EXAMPLE VI having 6 parts of stearic acid.

The invention is illustrated in the following examples:

    __________________________________________________________________________     TREAD STOCK                                                                    Functional Groups                                                                        --COOH         --OH, --COOH   --OH--COOH                             Source    Stearic Acid   Alfol 20+, Azelaic acid                                                                       Alfol 20+, Stearic acid                Stock     A(Control)     B              C                                      __________________________________________________________________________     SBR       490            490            490                                    Zinc Oxide                                                                               6              6              6                                      Flexamine G                                                                              2              2              2                                      Witco 127 0.80           0.80           0.80                                   Stearic Acid                                                                             2                                                                    RX 10920                 2                                                     RX 10921                                2                                      Santocure 2.40           2.40           2.40                                   Thionex   .40            .40            .40                                    Sulfur    5              5              5                                      __________________________________________________________________________     Cured at                                                                       292° F.                                                                           M300                                                                               TB  EB DURO                                                                               M300                                                                               TB  EB DURO                                                                               M300                                                                               TB  EB DURO                        __________________________________________________________________________     10 min.    650                                                                               2300                                                                               760                                                                               55   200                                                                               1100                                                                               820                                                                               48   600                                                                               2100                                                                               760                                                                               55                          20 min.   1575                                                                               2950                                                                               510                                                                               61  1525                                                                               2900                                                                               500                                                                               59  1600                                                                               2975                                                                               510                                                                               62                          30 min.   1700                                                                               2950                                                                               480                                                                               62  1775                                                                               2900                                                                               460                                                                               60  1700                                                                               2875                                                                               460                                                                               63                          40 min.   1800                                                                               2950                                                                               480                                                                               63  1775                                                                               2900                                                                               460                                                                               60  1800                                                                               2975                                                                               460                                                                               63                          60 min.   1800                                                                               2975                                                                               480                                                                               62  1825                                                                               3000                                                                               470                                                                               61  1750                                                                               2900                                                                               460                                                                               63                          __________________________________________________________________________      M300 = modulus at 300%.                                                        TB = tensile at break.                                                         EB = elongation at break.                                                      DURO = Durometer reading.                                                      Santocure = Ncyclohexyl-2-benzothiazole sulfenamide                            Witco 127 = Blend of waxy hydrocarbon                                          Flexamine G is a diarylamineketone reaction product.                           Thionex is tetramethylthiuram monosulfide.                                     RX 10920  Azelaic acid, 20%; longchain alcohol mixture (Alfol 20+), 80%.       RX 10921  Alfol 20+ 50% plus Stearic acid 50%                            

    __________________________________________________________________________     HOT PATCH                                                                      Functional Groups                                                                        --COOH         --OH, --COOH   --OH--COOH                             Source    Stearic acid   Alfol 20+, Azelaic acid                                                                       Alfol 20+, Stearic acid                Stock     D(Control)     E              F                                      __________________________________________________________________________     Natural rubber                                                                           200            200            200                                    Stearic acid                                                                             4                                                                    RX 10920                 4                                                     RX 10921                                4                                      Zinc oxide                                                                               24             24             24                                     Microwhite No. 50                                                                        120            120            120                                    Naugawhite                                                                               2              2              2                                      C-566     2              2              2                                      Rosin Oil No. 48                                                                         5              5              5                                      0150, Cushion                                                                            2.28           2.28           2.28                                   Pepton 65 0.30           0.30           0.30                                   A-1       9.50           9.50           9.50                                   Sulfur    9              9              9                                      __________________________________________________________________________     Cured at                                                                       260° F.                                                                           M300                                                                               TB  EB DURO                                                                               M300                                                                               TB  EB DURO                                                                               M300                                                                               TB  EB DURO                        __________________________________________________________________________      5 min.   225 1900                                                                               700                                                                               36  200 1350                                                                               640                                                                               34  200 1600                                                                               700                                                                               34                           7 min.   225 2050                                                                               720                                                                               37  225 1900                                                                               700                                                                               34  225 1825                                                                               700                                                                               35                           9 min.   250 2275                                                                               700                                                                               40  250 2100                                                                               680                                                                               36  250 2075                                                                               680                                                                               37                          12 min.   275 2050                                                                               650                                                                               41  275 2125                                                                               680                                                                               38  250 2150                                                                               680                                                                               39                          __________________________________________________________________________      Naugawhite is alkylated bisphenol.                                             A-1 is thiocarbanilide.                                                        Microwhite No. 50 is natural ground calcium carbonate                          Pepton 65 is zinc 2benzamidothiophenate                                  

    __________________________________________________________________________     RUBBER MAT                                                                     Functional Groups                                                                        --COOH         --OH,.sup.DI --COOH                                                                           --OH--COOH                                                      Alfol 20+, Azelaic acid                                                                       Alfol 20+, Stearic acid                Stock     G(Control)     H              I                                      __________________________________________________________________________     Butadiene-styrene                                                              rubber 173                                                                               150            150            150                                    AC Poly   2              2              2                                      Picco 6100                                                                               5              5              5                                      Witco 127 3              3              3                                      Stearic acid                                                                             1.50                                                                 RX 10920                 1.50                                                  RX 10921                                1.50                                   Zinc oxide                                                                               3              3              3                                      Micro-Fil No. 1                                                                          50             50             50                                     McNamee Clay                                                                             150            150            150                                    Amax      3              3              3                                      E. Tuads  0.80           0.80           0.80                                   Sulfur    3              3              3                                      Yellow MB 1              1              1                                      Blue 60   0.60           0.60           0.60                                   __________________________________________________________________________     Cured at  G              H              I                                      320° F.                                                                           M300                                                                               TB  EB DURO                                                                               M300                                                                               TB  EB DURO                                                                               M300                                                                               TB  EB DURO                        __________________________________________________________________________      5 min.   325 900 570                                                                               51  325 1000                                                                               670                                                                               50  400 900 550                                                                               51                           7 min.   350 750 520                                                                               51  350 875 580                                                                               51  400 850 530                                                                               51                           9 min.   350 725 510                                                                               51  350 750 540                                                                               51  400 825 500                                                                               51                          12 min.   325 700 510                                                                               51  350 800 530                                                                               51  400 800 500                                                                               51                          __________________________________________________________________________      Picco 6100 is a petroleum  hydrocarbon resin plasticizer.                      McNamee Clay is a soft kaolin clay.                                            E. Tuads is tetraethylthiuram sulfide.                                         Micro-Fil No. 1  solid mineral filler.                                         Amax is Noxydiethylene benzothiazole2-sulfenamide.                             AC Poly is a low molecular weight polyethylene manufactured by Allied          Chemical Company                                                         

DISCUSSION OF EXAMPLES I, II AND III EXAMPLE I

This example shows how an alcohol of this invention with added carboxylic groups from dibasic acid (Stock B) and a mixture of such an alcohol and stearic acid (Stock C) perform in an SBR recapping Tread Stock using stearic acid as a control (Stock A).

The stress strain data of the three stocks which were mixed and heated the same way show no differences which exceed experimental error. These three stocks were made in order to show up any differences which might appear due to the different functional groups present in the additives, e.g. stearic acid with the carboxyl group (--COOH), the hydroxyl group (--OH) with carboxylic group from a dicarboxylic acid, and the mixture of hydroxyl and carboxyl groups (--COOH, --OH) from long-chain alcohols and stearic acid.

In particular, attention is drawn to the 300% moduli data since this date is considered by some to be an accurate representation of the state of cure of a rubber compound. Since the data given are all within experimental error at 2950 psi±25 psi, it seems that all three compounds behave equivalently. Thus, long-chain alcohol seems equivalent to the stearic acid, and when carboxyl groups are added in the form of a dibasic acid, the effect is picked up by the 300% modulus reading.

A further study was made of these stocks by means of a Monsanto Rheometer, which can be used to measure the cure rate of rubber over a period of time. In these tests, which bring out the polymer curing characteristics in terms of twist or torque at a definite temperature (350° F. in all of these cases), the Rheometer shows that Stock C. containing the Alfol 20+ with added stearic acid behaves very much like the stearic acid Control A, whereas Stock B shows slightly less acceleration of cure by a few seconds. Stock B contains carboxyl group from azelaic acid. In fact, it is often desirable to have slightly less acceleration of cure for plant processing.

EXAMPLE II

Example II shows a series of three stocks, D, E and F, made with a ribbed smoked sheet natural rubber. Again, results at 300% modulus at the optimum cure times are within experimental error, except possibly the durometer hardness, which shows lower hardness values. These lower durometer values coupled with the excellent 300% modulus, tensile at break and elongation at break are often very desirable qualities.

The Rheometer tests reflect the same qualities obtained when the tread stock was tested. That is, (1) the alcohol-containing stocks E and F showed some influence on acceleration of cure rate, (2) the presence of some dicarboxyl group in Example E, showed somewhat more acceleration, and (3) the Stock F using alcohol and stearic acid showed the least acceleration of cure. The characteristic of this cure using the long-chain alcohol indicates a large safety factor in plant production. This longer processing produces elastomers with a superior combination of properties.

EXAMPLE III

This example shows the tests on a stock which is a high mineral-loaded rubber. This series shows up more differences, even though less stearic acid and alcohols are used in the formula or recipe.

Superior modulus at 300%, tensile at break and elongation at break properties are obtained in the examples using Alfol 20+.

The Rheometer curves obtained are the most marked by differences. As before, the acceleration was less, but the acceleration differed by 20-25 seconds where before the difference was only 4-8 seconds. Stock G, containing stearic acid, cured rapidly in 3 minutes. Stock H, containing dicarboxyl groups, took longest to cure, while Stock I, containing carboxyl and Alfol 20+, cured at a rate between the other two. The Stock I gave the best physicals of the three.

EXAMPLE IV

In another example using a natural rubber recipe, we test stearic acid against Epal 20+, a long chain alcohol mixture containing branch chains.

    ______________________________________                                         Recipe                                                                                             Parts                                                      ______________________________________                                         #1 Ribbed Smoke Sheet 100.0                                                    HAF Black             55.0                                                     Sun Par               20.0                                                     Ble 25                1.0                                                      Santocure NS*         0.7                                                      Sulfur                3.0                                                      ZnO                   5.0                                                      Fatty Acid or Epal C-20+                                                                             2.0                                                      Cure Temperature - 285° F.                                              ______________________________________                                          *Santocure NS = ntert-butyl-2-benzothiazole sulfenamide                  

    ______________________________________                                         Stock         J            K                                                   Additive      Stearic Acid Epal C-20+                                          ______________________________________                                         Cure Time, min.                                                                              20     30     45   20   30   45                                  300% Modulus  1750   2220   2400 1950 2090 2100                                Tensile       3470   3740   3640 3650 3740 3610                                Elongation    560    520    480  560  510  520                                 Shore Hardness                                                                               60     64     64   60   63   63                                  ______________________________________                                         Monsanto Rheometer                                                                         Torque                                                             3° arc, 3 cycles/min                                                    MPC dies: 30 sec.                                                                          min.      8.9        10.7                                          preheat, 60' motor                                                                         max.      86.4       73.8                                          ASTM D2084  scorch time                                                                    2 pt. TS2 8.8        9.1                                           ______________________________________                                    

Example IV shows that, by the use of a long chain alcohol only vs. a stearic acid, a natural rubber compound could be made having the same properties, but perhaps more importantly, the rheometer shows that the power requirements are much less. This benefit alone in this time of higher energy costs and lower energy availability makes the use of these long chain alcohols of major importance to industry and the country.

EXAMPLE V Diester of Long Chain Alcohols

In a test which was run exactly like Example IV, an ester was used in place of the long chain alcohol. The ester was code SAS 35, which was made by reacting 1 mole of dimethyl glutarate with 2 moles of Alfol 20+, thus yielding a long chain alcohol diester of glutaric acid, a dibasic acid.

When code SAS 35 was used in the same recipe as in Example IV, the results were similar to Example IV, especially in the low energy requirements used in processing.

EXAMPLE VI Long Chain Alcohol in a Synthetic Natural Rubber

In this example, we show the effect of Alfol 20+ in a synthetic natural rubber. The following recipe was used.

    ______________________________________                                                         Parts                                                          ______________________________________                                                Natsyn 400 100.0                                                               AnO        5.0                                                                 EPC Black  55.0                                                                Pine Tar   5.0                                                                 PBNA       1.0                                                                 Sulfur     2.25                                                                Durax      1.0                                                          ______________________________________                                    

                  TABLE I                                                          ______________________________________                                         Stock        L       M       N     0                                           ______________________________________                                         Alfol 20+    2.00            6.00                                              Stearic Acid         2.00          6.00                                        ______________________________________                                    

A rheograph was run (FIGS. 1 and 2) on four compositions as shown in Table I containing 2 and 6 parts of Alfol 20+ and stearic acid respectively. These show that at 2 parts of stearic acid vs. Alfol 20+, stearic acid acts like an accelerator as compared to Alfol 20+, but at the 6 part level, stearic acid acts as a retarder whereas Alfol 20+ acts as an accelerator even faster than stearic. Furthermore, stearic acid blooms in this recipe, and the Alfol 20+ does not. 

I claim:
 1. A natural or synthetic olefinic rubber composition comprising the rubber, sulfur and a vulcanization activating effective amount of a vulcanization activator for said rubber comprising an aliphatic polycarboxylic acid having 4 to 54 carbon atoms, wherein said activator is not volatile at 200° F. and has an acid number of at least
 50. 2. A composition as defined in claim 1 wherein said activator further includes an ester of an aliphatic alcohol having 12 to 28 carbon atoms and a carboxylic acid containing 4 to 54 carbon atoms and having a saponification number of at least
 50. 3. A composition as defined in claim 2 wherein said acid of said ester is a dicarboxylic acid or a tricarboxylic acid.
 4. A composition as defined in claim 2 wherein said carboxylic acid of said ester comprises an aliphatic polycarboxylic acid.
 5. A composition as defined in claim 1 wherein said rubber is vulcanized.
 6. A composition as defined in claim 1 wherein said rubber is unvulcanized.
 7. A composition as defined in claim 1 wherein said activator further includes an aliphatic alcohol having 12-28 carbon atoms.
 8. A natural or synthetic olefinic rubber composition comprising the rubber, sulfur and a vulcanization activating effective amount of a vulcanization activator for said rubber comprising a mixture of an aliphatic polycarboxylic acid having 4 to 54 carbon atoms having an acid number of at least 50 and an aliphatic alcohol having 12 to 28carbon atoms, and wherein said activator is not volatile at 200° F.
 9. A natural or synthetic olefinic rubber composition comprising the rubber, sulfur and a vulcanization activating effective amount of a vulcanization activator for said rubber comprising an ester of an aliphatic alcohol having 12 to 28 carbon atoms and an aliphatic polycarboxylic acid having 4 to 54 carbon atoms, said activator having a saponification number of at least
 50. 10. A composition as defined in claim 9 wherein said polycarboxylic acid is a dicarboxylic acid.
 11. A composition as defined in claim 9 wherein said rubber is vulcanized.
 12. A composition as defined in claim 9 wherein said rubber is unvulcanized.
 13. A natural or synthetic olefinic rubber composition comprising the rubber, sulfur and a vulcanization activating effective amount of a vulcanization activator for said rubber comprising an ester, having a saponification number of at least 50, formed by reacting an aliphatic alcohol having 12 to 28 carbon atoms with a carboxylic acid selected from the group consisting of butyric, valeric, hexanoic, hepanoic, octanoic, pelargonic, capric, undeconoic, lauric, myristic, palmitic, stearic, behenic, naphthenic, succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, dodecanedioic, brassylic, thapsic, phthalic, isophthalic, terephthalic, maleic, ##STR1## wherein one X is hydrogen and the other X is a carboxylic acid group, dimer oleic, aconitic, citric, tricarballylic, trimer oleic acid, trimellitic, and mixtures thereof.
 14. A natural or synthetic olefinic rubber composition comprising the rubber, sulfur and a vulcanization activating effective amount of a vulcanization activator for said rubber comprising an ester having a saponification number of at least 50 formed by reacting an aliphatic alcohol having 12 to 28 carbon atoms with a monocarboxylic acid.
 15. A composition as defined in claim 14 wherein said monocarboxylic acid is selected from the group consisting of butyric, valeric, hexanoic, hepanoic, octanoic, pelargonic, capric, undeconoic, lauric, myristic, palmitic, stearic, behenic, naphthenic, and mixtures thereof.
 16. A composition as defined in claim 14 wherein said acid is an aliphatic monocarboxylic acid. 